I understand that on Divine Mercy Sunday(meeting
the requirements), one's sins are forgiven and
punishment due to sins is expiated? But how does that
apply to one in prison - one still suffers in prison?
And even though repentant?

Answer by Judie Brown on 4/25/2014:

Paul

This quote is from Saint Faustina's Diary:

"On one occasion, I heard these words: My daughter, tell the whole world about My
Inconceivable mercy. I desire that the Feast of Mercy be a refuge and shelter for all souls, and
especially for poor sinners. On that day the very depths of My tender mercy are open. I pour
out a whole ocean of graces upon those souls who approach the fount of My mercy. The soul
that will go to Confession and receive Holy Communion shall obtain complete forgiveness of
sins and punishment.* [our emphasis] On that day all the divine floodgates through which
grace flow are opened. Let no soul fear to draw near to Me, even though its sins be as scarlet."